Unenhanced TIFF Sidescan-Sonar Mosaic of Las Vegas Wash - Lake Mead, Nevada: Geographic Coordinates

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Frequently-anticipated questions:

What does this data set describe?
    Title:
    Unenhanced TIFF Sidescan-Sonar Mosaic of Las Vegas Wash - Lake Mead, Nevada: Geographic Coordinates
    Abstract:
    Lake Mead is a large interstate reservoir located in the Mojave Desert of southeastern Nevada and northwestern Arizona. It was impounded in 1935 by the construction of Hoover Dam and is one of a series of multi-purpose reservoirs on the Colorado River. The lake extends 183 km from the mouth of the Grand Canyon to Black Canyon, the site of Hoover Dam, and provides water for residential, commercial, industrial, recreational, and other non-agricultural users in communities across the southwestern United States. Extensive research has been conducted on Lake Mead, but a majority of the studies have involved determining levels of anthropogenic contaminants such as synthetic organic compounds, heavy metals and dissolved ions, furans/dioxins, and nutrient loading in lake water, sediment, and biota (Preissler, et al., 1998; Bevans et al, 1996; Bevans et al., 1998; Covay and Leiker, 1998; LaBounty and Horn, 1997; Paulson, 1981). By contrast, little work has focused on the sediments in the lake and the processes of deposition (Gould, 1951). To address these questions, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the USGS in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology and the distribution and thickness of sediment that has accumulated in the lake since the completion of Hoover Dam. Results indicate that the accumulation of post-impoundment sediment is primarily restricted to former river and stream beds that are now submerged below the lake while the margins of the lake appear to be devoid of post-impoundment sediment. The sediment cover along the original Colorado River bed is continuous and is typically greater than 10 m thick through much of its length. Sediment thickness in some areas exceeds 35 m while the smaller tributary valleys typically are filled with less than 4 m of sediment. Away from the river beds that are now covered with post-impoundment sediment, pre-impoundment alluvial deposits and rock outcrops are still exposed on the lake floor.

  1. How should this data set be cited?

    Twichell, David C. , and Cross, VeeAnn A. , 2003, Unenhanced TIFF Sidescan-Sonar Mosaic of Las Vegas Wash - Lake Mead, Nevada: Geographic Coordinates:.

    Online Links:

    This is part of the following larger work.

    Twichell, David C. , Cross, VeeAnn A. , and Belew, Stephen D. , 2003, Mapping the floor of Lake Mead (Nevada and Arizona): Preliminary discussion and GIS data release: Open-File Report 03-320, U.S. Geological Survey, Woods Hole Field Center, Woods Hole, MA.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -114.877684
    East_Bounding_Coordinate: -114.805622
    North_Bounding_Coordinate: 36.139662
    South_Bounding_Coordinate: 36.109843

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 01-Jun-2000
    Ending_Date: 06-Jun-2000
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: remote-sensing image

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Raster data set. It contains the following raster data types:

      • Dimensions 3308 x 6468 x 1, type Pixel

    2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000009. Longitudes are given to the nearest 0.000011. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257224.

  7. How does the data set describe geographic features?

    Band_1

    ObjectID
    Internal feature number. (Source: ESRI)

    Sequential unique whole numbers that are automatically generated.

    Value

    Red

    Green

    Blue

    Entity_and_Attribute_Overview:
    The pixel value represents the DN return value of the sidescan-sonar system. A high value (ie 254) indicates a highly reflective lake floor surface, while a low value (ie 0) indicates low reflectance.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov

Why was the data set created?
This sidescan-sonar imagery is used to map the morphology of the lake floor and determine the extent of sediment distribution on the lake floor.

How was the data set created?
  1. From what previous works were the data drawn?

  2. How were the data generated, processed, and modified?

    Date: Jun-2000 (process 1 of 4)
    Sidescan sonar imagery was collected using an Edgetech DF1000 sidescan sonar system and logged to a Triton QMIPS data logging computer. All of the data were collected at a 200m swath, 1024 pixels/side, 16-bit. The digital sidescan data were then processed and mapped to provide proper geographic locations of features identified in the imagery. The processing steps included subsampling the raw sidescan data using a median filtering routine to suppress speckle noise and reduce file size, and corrrect for slant-range distortion, signal attentuation, and dropped sonar lines using XSonar (Danforth et al., 1991).

    Person who carried out this activity:

    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov

    Data sources used in this process:
    • Danforth, W.W., O'Brien, T.F., and Schwab, W.C., 1991, USGS image processing system: near real-time mosaicking of high-resolutoin sidescan-sonar data: Sea Technology, Jan., 1991, p. 54-59.

    Date: Jun-2000 (process 2 of 4)
    The imagery was mapped into its proper geographic location using techniques summarized by Paskevich (1996). Individual sidescan swaths were mapped with each pixel geographically positioned at a resolution of 1 m/pixel.

    Person who carried out this activity:

    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov

    Data sources used in this process:
    • Paskevich, V.F., 1996, MAPIT: An improved method for mapping digital sidescan sonar data using the Woods HOle Image Processing System (WHIPS) software: U.S. Geological Survey Open-File Report 96-281, 73p.

    Date: Jun-2000 (process 3 of 4)
    Non-overlapping swaths were then brought into the remote sensing software package PCI. The techniques for generating the composite digital sidscan mosaic are summarized by Paskevich (1992). The imagery portion was then cut out and written to a PCI channel with a white background. By doing this, within ArcView the user can turn the 255 pixel value to transparent and only display the actual sidescan imagery. This enhanced image was then exported from PCI as a TIFF image with an associated world file for georeferencing purposes.

    Person who carried out this activity:

    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    508-548-8700 x2266 (voice)
    508-457-2310 (FAX)
    dtwichell@usgs.gov

    Data sources used in this process:
    • Paskevich, V.F., 1992, Digital mapping of sidescan sonar data with the Woods Hole Image Processing System software: U.S. Geological Survey Open-File Report 92-536, 87p.

    (process 4 of 4)
    The UTM projected image was the reprojected to Geographic coordinates using BlueMarble's Geographic Transformer software. Transform parameters used a resolution of 1m/pixel and a central latitude of 36N.

How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?

  2. How accurate are the geographic locations?

    The ship was navigated with P-CODE GPS. The towfish was deployed at approximately the same depth each day, with little variation during the course of the survey. Due to the shipboard configuration, the navigation antennae was placed at the approximate layback position of the towfish, therefore range to fish errors are assumed to be negligible.

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    All imagery necessary to map the lake floor of interest in this particular study was used.

  5. How consistent are the relationships among the observations, including topology?

    All of these data were collected with the same sidescan-sonar towfish - the Edgetech DF1000. All data were collected as 16-bit, 200m swath, 1024 pixels/side.

How can someone get a copy of the data set?
Are there legal restrictions on access or use of the data?

Access_Constraints: None
Use_Constraints:
The U.S. Geological Survey must be referenced as the originator of the dataset in any future products or research derived from these data.

  1. Who distributes the data set? (Distributor 1 of 1)

    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov

  2. What's the catalog number I need to order this data set?

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

    These data were prepared by an agency of the United States Government. Neither the United States government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Although all data published in this report have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and/or the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of this data, software, or related materials.

  4. How can I download or order the data?

Who wrote the metadata?
Dates:
Last modified: 06-Oct-2003

Metadata author:
VeeAnn A. Cross
U.S. Geological Survey
Marine Geologist
384 Woods Hole Rd.
Woods Hole, MA 02543-1598

(508) 548-8700 x2251 (voice)
(508) 457-2310 (FAX)
vatnipp@usgs.gov

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

Metadata extensions used:

Generated by mp version 2.7.3 on Mon Oct 06 12:19:57 2003